Vertical monopole with spiral-shaped top loading



y 1, 1968 K. H. K 3,384,896

VERTICAL MONOPOLE WITH SPIRAL-SHAPED TOP LOADING Filed June 28, 1965 5Sheets-Sheet l INVENTOR. KAQL H. K1212 IF-J1EE:- a AT-rorzNay K. H. KRIZ3,384,896

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May 21, 1968 K. H. KRIZ 3,384,895

VERTICAL MONOPOLE WITH SPIRAL-SHAPED TOP LOADING Filed June 28, 1965 5Sheets-Sheet 3 INVENTOR. KARL H- KEIZ W BY U JVMML (1 AT-ro ENEY UnitedStates Patent 3,384,896 VERTICAL MONOPOLE WITH SPIRAL-SHAPED TOP LOADINGKarl H. Kriz, Northridge, Calif., assignor to Northrop Corporation,Beverly Hills, Calif., a corporation of California Filed June 28, 1965,Ser. No. 467,399 14 Claims. (Cl. 343713) This invention relates to atop-loaded spiral radio antenna, and more particularly to such anantenna which is readily transportable for field installation.

In receiving and transmitting radio waves at relatively low frequencies,vertical antennas are generally utilized in conjunction with theirground images to generate a strong ground wave which provides the mostefficient type of transmission at such frequencies. For optimum results,the vertical antenna should be a quarter-wave length at the operationalfrequency. Where very low frequencies are involved, the dimensions of aquarter-Wave length become so great as to make it impractical to providea vertical antenna section of such proportions. This problem isespecially diflicult in situations where the antenna must be set uptemporarily in the field and then moved to a subsequent location, as isoften the case where field military communication installations areinvolved. In order to lessen the amount of vertical antenna section thatis required, top loading is often utilized in antennas of the prior art.Such techniques sometimes involve the utilization of horizontal sectionsof antenna which may be folded back on each other so that the totalantenna length including the vertical section is equal to the desiredquarter Wave length. These horizontally oriented antenna sectionsprovide horizontally polarized radiation which does not contribute tothe ground wave and therefore provides no useful radiation, all of theeffective radiation being provided by the vertical section. The use ofthe top-loading section, however, brings about a desirable currentcondition in the vertical section of the antenna and thus provideseffective radiation of power therefrom.

When operating at very low frequencies (of the order of l0-2,000kilocycles) the horizontally oriented top loading section can take onenormous proportions, where vertical lengths which are of the order ofonly 305O feet are permissible. The device of this invention provides aradio antenna particularly suitable for utilization at low and very lowfrequencies which is readily transportable for erection in the field ina minimum amount of time and with a minimum effort. This end result isachieved by utilizing a top-loading section which is wound in thegeneral configuration of a tight spiral and which is supported on aframe which is foldable for ready transportation. In a preferredembodiment of the invention, the frame is supported on a verticaljacking device which is mounted on a truck and the top loading sectionmay thus be folded and mounted on the truck and then rapidly installedin the field. Means are further provided in the device of the inventionto utilize various lengths of the top loading spiral section to make forquarter wave resonance at various frequencies, thus enabling rapidchanges of resonant fre quency as operational requirements may dictate.

The device of this invention thus enables efficient low frequencyantenna operation in the form of a portable type installation, suitablefor ready assembly and disassembly in the field.

It is therefore an object of this invention to provide an improved radioantenna utilizing top loading in the form of a generally spiral woundhorizontal section.

It is still a further object of this invention to enable more efficienttransmission of low frequency radio waves in portable installations.

3,384,896 Patented May 21, 1968 It is still another object of thisinvention to provide an eificient low frequency antenna which issuitable for mounting on a vehicle.

It is still another object of this invention to provide a top loadedantenna having relatively high efficiency which is particularly suitablefor temporary installations.

Other objects of this invention will become apparent from the followingdescription taken in connection with the accompanying drawings, ofwhich:

FIG. 1 is an elevation view illustrating the device of the invention asinstalled on a truck,

FIG. 2 is a top plan view of the installation shown in FIG. 1,

FIG. 3 is a perspective view illustrating a preferred embodiment of thedevice of the invention,

FIG. 4 is a perspective view showing an alternative spiral top loadingsection which may be utilized in the device of the invention,

FIG. 5 is a schematic view illustrating a tuning device that may beutilized in the device of the invention,

FIG. 6 is a cross-sectional view as taken along the plane indicated by6--6 in FIG. 3,

FIG. 7 is a partial top plan view illustrating the details ofconstruction of the top-loading member shown in FIG. 3, and

FIG. 8 is a view of the bracket assembly of the support member shown inFIG. 7 as taken along the plane indicated by 8-8 in FIG. 7.

Referring now to FIGS. 3 and 68, a first embodiment of the device of theinvention is illustrated. Frame member 11, which is preferablyfabricated of a material having a high strength to weight ratio, such asFiberglas, includes two end portions 11a and 11b and a central portion11c. End portions 11a and 11b are pivotally joined to central portion bymeans of hinge members 12. End portions 11a and 11b are shorter in widththan central portion 11c so that they may be folded over on top of thecentral portion to make for a more readily transportable package.

Strung on frame 11 is web 14 fabricated of a flexible insulatingmaterial, such as glass cloth. Wound on webbing 14 and attached theretoby suitable means, such as, for example, nylon stitching or cementing,is top loading antenna section 17 which is wound in the general form ofa spiral. The spiral form may be in the general form of a square orrectangle, as shown in FIGS. 3 and 7, or may be in the curved shape of atrue spiral. Top loading sec tion 17 thus starts at a point 20 near thecenter of web portion 14 and winds outwardly in one direction toward theouter portion of web 14 where it finally terminates at point 21. Thewire portions of top loading section 17 are fabricated of a highlyconductive electrically conductive material such as copper and areattached to web portion 14 so that the individual windings thereof areadequately insulated from each other to assure that the electrical pathformed thereby follows the spiral windings. This end result may beachieved by utilizing wire having an insulated covering thereon.

The starting point 20 of the spiral winding is grounded by means oflines 24, which provide the vertical section from which the effectiveradiation occurs. Feed line 25 which couples the antenna to thetransmitter or receiver is connected to the spiral windings at point 27.Point 27 is spaced from point 20 a distance which provides an optimumimpedance match which is determined experimentally for each antennadesign by techniques known to those skilled in the art. Transmitting andreceiving equipment (not shown) is coupled to feed line 25 by means ofcoaxial cable 30.

For illustrative purposes, a shunt feeding technique is shown in FIG. 3,i.e., with point 20 connected to lines 24 which are grounded, and feedline 25 connected at a point 27 spaced from point 20. If so desired,however, a series feed can be utilized with feed line 25 connecteddirectly to central point 20 and line 24 eliminated. In this case, ofcourse, feed line 25 will form the radiating element.

In order to enable resonant operation of the antenna at severaloperating frequencies, the spiral top loading windings 17 areinterrupted at points 35a35d by dual lines 36a-36d which run to controlbox 37. Referring to FIG. 5, control box 37 includes a plurality ofswitches 40a40d, by means of which the total effective electrical lengthof the spiral top loading section 17 can be changed to provide resonanceat various operating frequencies. Control box 37 also has tuningcapacitors 45a45d for precise tuning of each of the antenna sections.Thus, for example, with all of the switches in the positions indicated,the entire length of the top loading section is utilized providingresonance at the lowest operating frequency. The highest resonantfrequency is obtained by closing switch 40a, while other operatingfrequencies may be achieved by means of switches 40b, 40c and 40d. Shunttuning capacitors 4511-4511 may be utilized to tune the antenna. If sodesired, a series tuning capacitor may be added in the top-loadingspiral section, such modification being within the capabilities of oneskilled in the art.

Central support frame section 110 includes beefed up members 18 and 19to assure proper strength and rigidity of the overall structure.

Referring now to FIGS. 6 and 7, details of structure of the supportframe and web portion are illustrated. Web portion 14 includes webstrands 50, the ends of which are looped around frame 11 and arestretched on the frame and attached thereto by means of stitching 51.The spiral wire portion 17 is wound on webbing 14 and attached theretoby means of nylon thread, cementing or any other suitable means. It isessential, however, that the individual wires be adequately separated orotherwise insulated from each other so that no short circuiting canoccur between adjacent wire sections. This problem may be completelyavoided by utilizing insulated wire.

Referring now to FIG. 8, a hinge mechanism utilized in the firstembodiment of the device of the invention is shown. Locking plate 58 isfixedly attached to hinge plate 57 which in turn is fixedly attached toframe section 11b, while locking pin 61 is fixedly attached to hingeplate 60, which in turn is fixedly attached to frame section 110. Thus,with locking pin 61 released, frame section 11b can be folded over ontoframe section 110. With frame section 11b out in its extended position,the two frame sections are locked in this position by means of lockingpin 61 which engages an appropriate slot 63 formed in locking plate 58.

Referring now to FIG. 4, a second embodiment of the device of theinvention utilizing a plurality of spiral top loading sections ratherthan a single such section is illustrated. In this embodiment, ratherthan utilizing a single spiral section 17, a plurality of small spiralsections 17a- 171 connected in series are utilized. These spiralsections are attached to web portion 14 in the same fashion as singlespiral section 17, and may utilize a similar tuning mechanism andcoupling to the vertical section as described in connection with FIG. 3.While the single spiral configuration shown in FIG. 3 operates toeffectively cancel out horizontally polarized energy, thus assuring thatmost of the radiation occurs from vertical lines 24, at certainoperating frequencies a resonant condition may be set up in this singlespiral section which may result in undesirable losses therein. In suchinstances, the utilization of a plurality of small spiral sections, eachof which tends to have a high resonant frequency, as compared to theoperational frequency, minimizes the chances of such undesirableresonant effects occurring in the top-loading section.

Referring now to FIGS. 1 and 2, a typical installation of the device ofthe invention is shown. Frame 11 is mounted on telescoping supports 66.Supports 66 are mounted on truck 65. Hydraulic jacking means (not shown)are utilized to raise and lower support sections 66 so that frame 11 maybe lowered down on to truck 65 for transportation. In the installedposition, as shown, frame 11 is guyed by means of guy wires 70. A groundplane is provided by means of ground mat 75, over which the antennaframe 11 is positioned. Ground mat may include a series of overlappingstrip portions 76 fabricated of copper wire mesh, these strip portionsbeing rolled out so that they overlap each other. The ground mat 75,which forms a ground plane for the antenna, is effectively extended andconnected to the earth by means of radially extending wires 80 which arestaked into the ground. Thus, as can be seen, a transportableinstallation is provided which can readily be dismantled and moved to anew location as the situation may demand.

The device of the invention thus provides a comparatively efiicientradio antenna which is relatively compact in configuration. Thisantenna, while ideally suited for use at low operation frequencies, canalso be used to advantages on higher frequencies where space and size isa factor. The antenna of the invention is particularly adaptable for amobile field installation, in whichcase it can be moved to a newlocation in a minimum amount of time and with a minimum amount ofeffort.

While the device of the invention has been described and illustrated indetail, it is to be clearly understood that this is intended by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of this invention being limited only bythe terms of the following claims.

I claim:

1. A radio antenna comprising a vertical antenna section,

a top-loading antenna section connected to one end of said verticalantenna section, comprising a substantially horizontally orientedgenerally spirally wound wire portion,

means for supporting said top-loading section comprising a frame member,a webbing fabricated of electrically insulating material strung on saidframe member, means for attaching said top-loading antenna section tosaid webbing portion, and means for supporting said frame membersubstantially horizontally over the ground, and

means for coupling said antenna to a radio frequency device,

whereby said vertical antenna section and said toploading section ascombined resonate at a predetermined operating frequency withsubstantially all the electromagnetic radiation of said antenna beingradiated from said vertical antenna section.

2. The antenna as recited in claim 1 wherein said toploading wireportion and said webbing are flexible and said frame member is foldable.

3. The antenna as recited in claim 1 wherein said vertical antennasection comprises wire means connected at one end thereof to theinternal end of said spirally wound wire portion, the other end of saidwire means being connected to the ground.

4. The antenna as recited in claim 3 wherein said Wire means comprises aplurality of radially and downwardly extending wires.

5. The antenna as recited in claim 1 and further including means forchanging the effective length of said toploading section.

6. The antenna as recited in claim 5, wherein said means for changingthe effective length of said top-loading section includes a plurality ofdual wire lines for interrupting said loading section at predeterminedpoints and switch means for selectively connecting the wires ofpreselected ones of said dual lines together.

7. The antenna as recited in claim 1, wherein said means for supportingsaid frame member comprises a vehicle and support means mounted on saidvehicle for raising said frame member above said vehicle and lower-- ingsaid frame member onto said vehicle for transportation.

8. The antenna as recited in claim 1 and further including a Wire meshmat laid on the ground beneath said top-loading section to form a groundplane.

9. The antenna as recited in claim 3, wherein said means for couplingsaid antenna to a radio frequency device comprises an electricallyconductive feed line attached to the spirally wound wire portion at apoint which is a predetermined distance from the internal end of saidwire portion.

10. A radio antenna comprising a vertical antenna section,

a top-loading antenna section connected to one end of said verticalantenna section, comprising a substantially horizontally orientedgenerally spirally wound flexible wire portion,

means for supporting said top-loading section comprising a foldableframe member, a flexible webbing fabricated of electrically insulatingmaterial strung on said frame member, means for attaching saidtoploading antenna section to said webbing portion, and means forsupporting said frame member substantially horizontally over the ground,said frame member including three sections, and hinge means for joiningsaid three sections together in foldable relationship, and

means for coupling said antenna to a radio frequency device,

whereby said vertical antenna section and said toploading section ascombined resonate at a predetermined operating frequency withsubstantially all the electromagnetic radiation of said antenna beingradiated from said vertical antenna section.

11. The antenna as recited in claim 10, wherein said vertical antennasection includes a plurality of radially extending wires attached at oneend thereof to the internal end of said spirally wound wire portion andat the other end thereof to the ground.

12. The antenna as recited in claim 11 wherein said means for couplingsaid antenna to a radio frequency device comprises a feed line connectedto said spirally wound wire portion at a point which is a predetermineddistance from the internal end thereof.

13. A radio antenna comprising a vertical antenna section,

a top-loading antenna section connected to one end of said verticalantenna section, comprising a plurality of substantially horizontallyoriented generally spirally wound antenna portions, said top-loadingantenna portions being connected in series, and

means for supporting said top-loading section comprising a frame member,a flexible webbing fabricated of electrically insulating material strungon said frame member, means for attaching said top-loading antennaportions to said webbing portion, and means for supporting said framemember substantially horizontally over the ground, said frame memberinclud ing three sections, and hinge means for joining said threesections together in foldable relationship,

whereby said vertical antenna section and said top loading section ascombined resonate at a predetermined operating frequency withsubstantially all the electromagnetic radiation of said antenna beingradiated from said vertical antenna section.

14. The antenna as recited in claim 13 wherein said vertical antennasection comprises a plurality of downwardly and radially extending Wiremembers, one end of each of said wire members being connected to theinternal end of said top-loading section, the other ends of said wiremembers being grounded.

References Cited UNITED STATES PATENTS 2,647,211 7/1953 Smeby 343-4522,964,748 12/1960 Radford 343874 2,998,604 8/1961 Seeley 343-8743,129,427 4/1964 Dunlavy 343-895 ELI LIEBERMAN, Primary Examiner.

1. A RADIO ANTENNA COMPRISING A VERTICAL ANTENNA SECTION, A TOP-LOADINGANTENNA SECTION CONNECTED TO ONE END OF SAID VERTICAL ANTENNA SECTION,COMPRISING A SUBSTANTIALLY HORIZONTALLY ORIENTED GENERALLY SPIRALLYWOUND WIRE PORTION, MEANS FOR SUPPORTING SAID TOP-LOADING SECTIONCOMPRISING A FRAME MEMBER, A WEBBING FABRICATED OF ELECTRICALLYINSULATING MATERIAL STRUNG ON SAID FRAME MEMBER, MEANS FOR ATTACHINGSAID TOP-LOADING ANTENNA SECTION TO SAID WEBBING PORTION, AND MEANS FORSUPPORTING SAID FRAME MEMBER SUBSTANTIALLY HORIZONTALLY OVER THE GROUND,AND MEANS FOR COUPLING SAID ANTENNA TO A RADIO FREQUENCY DEVICE, WHEREBYSAID VERTICAL ANTENNA SECTION AND SAID TOPLOADING SECTIONS AS COMBINEDRESONATE AT A PREDETERMINED OPERATING FREQUENCY WITH SUBSTANTIALLY ALLTHE ELECTROMAGNETIC RADIATION OF SAID ANTENNA BEING RAIATED FROM SAIDVERTICAL ANTENNA SECTION.